Any conditioned response is the expression of a specialized learning system with evolutionary and neurological significance. Gustatory cues are effective signals (CS) when paired with internal visceral consequences (US), but ineffective when paired with peripheral pain (US). On the other hand, telereceptive (visual-auditory) cues (CS) are effective for peripheral pain, but not for changes in internal states. Brain stem emetic areas mediate the acquisition and retention of conditioned taste aversions. Anti-emetic drugs block the expression of lithium-induced aversions, and subdiaphragmatic vagotomy blocks the acquisition of copper-sulfate-induced aversions, dependent upon the route of drug administration. We are using the pharmacologic and vagotomy preparations in buzzershock learning to characterize the anatomical substrates of these two conditioning systems. We are also determining the behavioral roles of olfaction of rats. Olfaction serves a dual function, being involved in both food selection and peripheral defense. However, if odor is conditioned in compound with taste, odor now becomes as strong as taste. Taste potentiates odor. We are using behavioral preparations to test the hypothesis that taste indexes odor as a feeding cue, which mediates an illness-induced odor aversion.